I. Field of the Invention
The present invention relates to a reprogrammable lock assembly and, in particular, to a reprogrammable lock which includes additional means of preventing unauthorized release of the lock and can only be programmed by a specific program key and unlocked by a specific use key.
II. Description of the Prior Art
Key-operated locks have been utilized for many years to provide limited access. The most widely utilized key-operated lock is of the tumbler/follower type manufactured to fit a particular key and each lock may be operated only by that key. Thus, in the early locks, the internal mechanism is configured to fit a particular key and cannot be changed unless the lock is taken apart and the followers reset with respect to the tumblers.
More recently, tumbler/follower locks have been developed which can be reprogrammed by adjusting the relative position of the follower and tumbler such that a different key must be used to operate the lock. In such locks, reprogramming is accomplished by rotating in a first direction while unlocking is accomplished by rotating in a second direction from a reference position. In the prior known reprogrammable lock, the prior use key is utilized to rotate the plug counterclockwise to a reprogram position and removed. Thereafter, the new use key is inserted and the lock is returned to the reference position thereby resetting the tumblers. This new use key can now be utilized to unlock the lock. The disadvantage of such an arrangement is that the casual user could inadvertently reprogram the lock since their key will move the lock to the reprogramming position. Such a possibility is highly undesirable in commercial settings such as hotels. It is desirable to have separate programming and use keys in order to precisely control operation of the lock.
Other lock assemblies utilize different keys to reprogram and to unlock the lock. One such assembly incorporates a plurality of shear pins to control rotation of the plug. The lock utilizes a reset key to move the lock to the reprogram position, a set key to reprogram the lock, and a use key to unlock the lock. However, the operation of the lock is limited because the programming can only be accomplished through a specific sequence of keys. Once the sequence is used up, the lock can no longer be reprogrammed. Moreover, the pin-type locks provide no means of preventing the lock from being picked.